linux-kernel - Re: [PATCH] driver core / ACPI: Avoid device removal locking problems

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Message-ID: <20130827183644.GC12212@mtj.dyndns.org>
Date:	Tue, 27 Aug 2013 14:36:44 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Gu Zheng <guz.fnst@...fujitsu.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Toshi Kani <toshi.kani@...com>,
	LKML <linux-kernel@...r.kernel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Subject: Re: [PATCH] driver core / ACPI: Avoid device removal locking problems

Hello,

On Tue, Aug 27, 2013 at 05:21:44PM +0800, Gu Zheng wrote:
> >> OK, so the patch below is quick and dirty and overkill, but it should make the
> >> splat go away at least.
> > 
> > And if this patch does make the splat go away for you, please also test the
> > appended one (Tejun, thanks for the hint!).
> > 
> > I'll address the ACPI part differently later.
> 
> What about changing device_hotplug_lock and acpi_scan_lock to rwsem? like the
> attached one(With a preliminary test, it also can make the splat go away).:)

Hmmm.. I don't get it.  How is introducing another rwlock whic may
cause the operation, even reading the status, to fail randomly a
better option?  It's harier and more brittle.  We probably want to
implement better solution in sysfs for files which interact with
device addition / removal paths but for now I think Rafael's patch is
the right direction.

Thanks.

-- 
tejun
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